Modern warfare frequently involves multiple branches of the military working in cooperation, and high speed and high data rate communications between the acting forces during unpredictable conditions in hostile environments is frequently necessary. Time critical targets need to be neutralized quickly. The ability to communicate high-resolution images at a very high data rate is often required. To perform and execute military missions, the effectiveness of such communications often depends on, for example, a real time data link. In another example, high-resolution intelligence surveillance and reconnaissance (ISR) images distributed by the satellite global broadcast system (GBS) may be required. In many of these situations, stealth is paramount. The sensor or communication system should not reveal the location of recipient forces or ships or otherwise compromise an operation.
Underwater vessels such as submarines often form an integral part of the battlefield scenario. Submarines can aid a variety of missions and deployment scenarios including neutralizing targets, support of special operations forces and clandestine missions, as well as enhancing linkage to other theater assets.
Submarines provide mobility, stealth and endurance for military operations. However, in the littorals or coastal regions near the sea surface, at slow speed, the probability of the submarine being detected increases and the consequences of detection are magnified. Therefore, it is advantageous for the submarine to have the ability to communicate while at sufficient depth and speed to maintain stealth and while carrying on mission functions.
Sea-based communications enable submarine participation in the battlefield scenario. High bandwidth satellite communication (SATCOM) is one enabler for submarine participation in the battlefield scenario, such as time-critical Network Centric Warfare (NCW) operations. Existing options for such communications, however, offer either high data rate communications with an antenna exposed such as for SATCOM reception/and or transmission, or stealth (with very low data rates), but not both. Known sea-based communication systems, particularly for high bandwidth submarine communications, have included mast-mounted antennas that are deployed and retracted from the submarine sail. However, deployment from the submarine sail has several drawbacks. The limited length of the mast requires that the submarine operate at relatively shallow periscope depths for extended periods of time. Wakes generated by the mast can be detectable for miles. Thus, the safety of the mission and the submarine can be compromised. Finally, the size (and hence, data rate) of retractable mast mounted SATCOM antennas are limited.
Alternatively, a variety of unmanned underwater vehicles (UUVs) have been developed or are under development for establishing communications for submerged submarines. UUVs are capable of carrying out a number of sophisticated tasks and may provide for multiple roles, i.e., communication and reconnaissance. Such systems, however, typically have a number of disadvantages. A UUV can maintain its attitude in wave motion near the surface only by operating above some minimum speed. This limits the life of the battery that powers the UUV. Also, the UUV creates a small wake which increases its detectability. Moreover, the UUV must be able to support an antenna large enough to receive GBS at a high data rate, and it must be high enough out of the water to avoid frequent sea wave upsets. To achieve these requirements, a moderately large UUV is required, at high cost. Additionally, recovery of an expensive and relatively large UUV diverts the submarine from its primary mission, and incurs additional risk of detection.
Traditional spar buoy designs are typically very large, stiff floating platforms comprising a large mass with significant righting moments. These spar buoys serve as large work platforms or data collection/telemetering buoys. One example is the ODAS Italia 1 spar buoy, which is approximately 150 feet in length with 24,000 pounds displacement. An open sea laboratory for oceanographic studies is one use of the ODAS Italia 1 spar buoy. Such designs, however, must be radically rescaled for uses where qualities such as small size and stealth are necessary or desired.
A surface floating buoy, even with deployed outriggers, also has disadvantages especially if used for communications purposes. It provides a poor platform for a stabilized antenna that must maintain its beam on a satellite in rough seas and high winds. The antenna must be high enough to minimize wind effects and wave washover, and the buoy must be large enough that wind drag on the elevated antenna will not upset it. These factors make a surface floating buoy too large for the intended purposes.
Retrievable buoys constitute another type of known buoy for use in submarine communications systems. Retrievable buoys are of modest size and may include a directional antenna on the top end. The retrievable buoy is released from a cradle on the deck a submarine, aft of the sail, and carries a data and recovery cable with it. This retrievable buoy system has a number of disadvantages. First, the concept calls for two such retrievable buoys, so that one may be active while the other is being retrieved and re-launched. Frequent release and retrieval activity produces acoustic signatures and increase the probability of detection, which is undesirable. Also, the system does not provide wideband communications at depth and speed because the buoy will reach the surface only if neither depth nor speed is excessive. Moreover, the size of the antenna that can be enclosed in the top of the retrievable buoy is too small to receive some types of communications such as wide-band GBS reception. In addition, the motion of the submarine only allows for data gathering until the data and recovery cable is depleted, which is only a few minutes due to the limited length of cable available because the cable must be strong enough to retrieve the retractable buoy. At that point, communications are interrupted and the retrievable buoy is pulled underwater and back into its cradle on the submarine.